The field of the invention relates to oscillators and more particularly to temperature controlled crystal oscillators.
For generating frequency reference signals in radio telephones and pagers, quartz crystal based oscillators predominate. Quartz crystal resonators offer several comparative advantages; they are inert, relatively power efficient, frequency stable and size scalable. However advantageous, crystal resonators present some practical problems. When quartz crystal is manufactured in an economical manner, its resonant frequencies cannot be predicted (or controlled) with an accuracy sufficient for many applications. Furthermore, the oscillating frequency of known quartz crystals is temperature dependantxe2x80x94the sensitivity varying according to crystal cut and crystal quality generally.
Accordingly, crystal oscillator circuits are both factory tuned to account for manufacturing variances and also equipped with features for temperature compensation. In the basic circuit design, an inverter and biasing resistor are each connected in parallel with the crystal resonator. The inverter and biasing resistor serve to start and then maintain the oscillation. An adjustable capacitance element such as a varactor or switched capacitor arrays are connected to the quartz crystal to allow frequency adjustment for factory tuning and temperature compensation. A voltage responsive temperature sensing element is scaled and operably connected to the adjustable capacitance element to provide temperature compensation of the oscillator frequency.
This frequency adjustment is conventionally called xe2x80x9cwarpingxe2x80x9d or xe2x80x9cpulling,xe2x80x9d labels which reflect the relative difficulty in changing the frequency of crystal-based oscillators. Although such crystal-based oscillator circuits have received widespread commercial acceptance, efforts at improvement on this basic design continued.
In the interest of allowing wireless communication providers to provide additional service, governments worldwide have allocated new higher RF frequencies for commercial use. To better exploit these newly allocated frequencies, standard setting organizations have adopted bandwith specifications with compressed transmit and receive bands as well as individual channels. These trends are pushing the limits of oscillator technology to provide sufficient frequency selectivity.
Coupled with the tighter frequency control requirements are the consumer market trends towards ever smaller wireless communication devices (.e.g. handsets) and longer battery life. Combined, these trends place difficult constraints on the design of wireless components such as oscillators. Oscillator designers may not simply add more space-taking components or increase power dissipation in order to provide improved accuracy and stability.
Therefore, the need continues for improved oscillators which can offer frequency selectivity, size reduction and other performance improvements.
A method and apparatus are provided for constructing a temperature controlled crystal oscillator chip. The method includes the steps of disposing a connection pad on a surface of the chip, providing a first circuit within the chip for control of a first chip function through a first interconnection with the connection pad and providing a second circuit within the chip for control of a second chip function, unrelated to the first chip function, through a second interconnection with the connection pad.